1. Field of Invention
The field of the currently claimed embodiments of this invention relates to systems and methods of obtaining spatially localized nuclear magnetic resonance parameters.
2. Discussion of Related Art
There are many parameters that can be measured by nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) including nuclear spin density, longitudinal relaxation time (T1) (1), longitudinal relaxation time in the rotating frame (T1ρ) (2), transverse relaxation time (T2) (1), the inhomogeneously broadened—T2, T2*, relaxation time (3), apparent diffusion coefficients (ADC) (4), perfusion measures (5), functional MRI (fMRI) measures (6), spectral parameters (7), chemical reaction rates (8), magnetization transfer ratios (9), and chemical exchange saturation transfer (CEST) indices (10), etc, using hydrogen (1H), carbon (13C), fluorine (19F), sodium (23Na) and phosphorus (31P) nuclei to name a few. These measures can derive from endogenous compounds present in biological systems, or from exogenous substances or tracers introduced into the system for the purpose of providing diagnostic, prognostic and/or therapeutic information.
In heterogeneous systems, such as the human body, animals or experimental animal models, these parameters are nonuniformly distributed, and therefore it is desirable to obtain measures that are localized to smaller partitions or regions of the system, such as an organ, a lesion, a pathology, or a region from which NMR or MRI information is being sought, within the organ. The standard way to achieve this is MRI which can provide a nearly continuous distribution of the parameters throughout the sample, limited only by the voxel resolution of the image and/or the time required for the scan. However, often there is inadequate time to provide images of the desired parameter at high image resolution due to insufficient signal-to-noise ratio (SNR), insufficient scan time when other clinical information must be acquired during an exam, for example, in the case of patient studies etc. In addition, image voxels acquired by MRI are rectangular and do not conveniently conform to arbitrarily-shaped compartments that coincide with the morphology of an organ or pathology of interest, such that simply increasing the image voxel size does not provide adequate coverage of the desired volume from which the parametric information is being sought, due to overlap of the rectangular voxel with other tissues, for example.
Consequently, there remains a need for systems and methods that can obtain NMR or MRI parameters such as those noted above for at least compartments of interest much more rapidly than measures obtained with conventional NMR and MRI systems and methods.